P. A. B. Galli

THE GOULD’S BELT DISTANCES SURVEY (GOBELINS). II. DISTANCES AND STRUCTURE TOWARD THE ORION MOLECULAR CLOUDS

We present the results of the Goulds Belt Distances Survey of young star-forming regions toward the Orion Molecular Cloud Complex. We detected 36 young stellar objects (YSOs) with the Very Large Baseline Array, 27 of which have been observed in at least three epochs over the course of two years. At least half of these YSOs belong to multiple systems. We obtained parallax and proper motions toward these stars to study the structure and kinematics of the Complex. We measured a distance of 388 ± 5 pc toward the Orion Nebula Cluster, 428 ± 10 pc toward the southern portion L1641, 388 ± 10 pc toward NGC 2068, and roughly ~420 pc toward NGC 2024. Finally, we observed a strong degree of plasma radio scattering toward λ Ori.

The Gould's Belt Distances Survey (GOBELINS). I. Trigonometric Parallax Distances and Depth of the Ophiuchus Complex

We present the first results of the Goulds Belt Distances Survey (GOBELINS), a project aimed at measuring the proper motion and trigonometric parallax of a large sample of young stars in nearby regions using multi-epoch Very Long Baseline Array (VLBA) radio observations. Enough VLBA detections have now been obtained for 16 stellar systems in Ophiuchus to derive their parallax and proper motion. This leads to distance determinations for individual stars with an accuracy of 0.3 to a few percent. In addition, the orbits of six multiple systems were modelled by combining absolute positions with VLBA (and, in some cases, near-infrared) angular separations. Twelve stellar systems are located in the dark cloud Lynds 1688; the individual distances for this sample are highly consistent with one another and yield a mean parallax for Lynds 1688 of ω = 7.28 ± 0.06 mas, corresponding to a distance d = 137.3 ± 1.2 pc. This represents an accuracy greater than 1%. Three systems for which astrometric elements could be measured are located in the eastern streamer (Lynds 1689) and yield an estimate of ω = 6.79 ± .016 mas, corresponding to a distance d = 147.3 ± 3.4 pc. This suggests that the eastern streamer is located about 10 pc farther than the core, but this conclusion needs to be confirmed by observations of additional sources in the eastern streamer (currently being collected). From the measured proper motions, we estimate the one-dimensional velocity dispersion in Lynds 1688 to be 2.8 ± 1.8 and 3.0 ± 2.0 km s^(−1), in R.A. and decl., respectively; these are larger than, but still consistent within 1σ of, those found in other studies.

A kinematic study and membership analysis of the Lupus star-forming region

Aims. A precise determination of the distance to individual stars is required to reliably determine the fundamental parameters (mass and age) of young stellar objects. This paper is dedicated to investigating the kinematic properties of the Lupus moving group of young stars with the primary objective of deriving individual parallaxes for each group member. Methods. We identify those stars in the Lupus star-forming region that define the comoving association of young stars by utilizing our new and improved convergent point search method that allows us to derive the precise position of the convergent point of the comoving association from the stars’ proper motions. We used published proper motion catalogs and searched the literature for radial velocities, which are needed to compute individual parallaxes. We supplemented the radial velocity data with new measurements from spectroscopic observations performed with the FEROS spectrograph mounted on the MPG/ESO 2.2 m telescope at La Silla. Results. We identify a comoving group with 109 pre-main sequence stars and candidates that define the kinematic properties of the Lupus low-mass star-forming region. We derive individual parallaxes for stars with known radial velocity and tentative parallaxes for the remaining group members by assuming that all stars share the same space motion. The convergent point method, combined with the k-NN algorithm, makes it possible to distinguish the Lupus and Upper Centaurus Lupus stars from the adjacent ScorpiusCentaurus association. We find significant depth e ects in this region and show that the classical T Tauri stars, located in the close vicinity of the Lupus molecular clouds, form a background population, while the weak-emission line T Tauri stars are dispersed not only in angular extent but also in depth. Conclusions. The newly derived individual parallaxes will be used in a forthcoming paper to refine the masses and ages of Lupus T Tauri stars, with the aim of better constraining the lifetimes of their circumstellar, protoplanetary disks.

The Gould's Belt Distances Survey (GOBELINS). III. The Distance to the Serpens/Aquila Molecular Complex

We report on new distances and proper motions to seven stars across the Serpens/Aquila complex. The observations were obtained as part of the Goulds Belt Distances Survey (GOBELINS) project between 2013 September and 2016 April with the Very Long Baseline Array (VLBA). One of our targets is the proto-Herbig AeBe object EC 95, which is a binary system embedded in the Serpens Core. For this system, we combined the GOBELINS observations with previous VLBA data to cover a total period of 8 years, and derive the orbital elements and an updated source distance. The individual distances to sources in the complex are fully consistent with each other, and the mean value corresponds to a distance of 436.0 ± 9.2 pc for the Serpens/W40 complex. Given this new evidence, we argue that Serpens Main, W40, and Serpens South are physically associated and form a single cloud structure.

A new method for calculating the convergent point of a moving group

Context. Convergent point (CP) search methods are important tools for studying the kinematic properties of open clusters and young associations whose members share the same spatial motion. Aims. We present a new CP search strategy based on proper motion data. We test the new algorithm on synthetic data and compare it with previous versions of the CP search method. As an illustration and validation of the new method we also present an application to the Hyades open cluster and a comparison with independent results. Methods. The new algorithm rests on the idea of representing the stellar proper motions by great circles over the celestial sphere and visualizing their intersections as the CP of the moving group. The new strategy combines a maximum-likelihood analysis for simultaneously determining the CP and selecting the most likely group members and a minimization procedure that returns a refined CP position and its uncertainties. The method allows one to correct for internal motions within the group and takes into account that the stars in the group lie at different distances. Results. Based on Monte Carlo simulations, we find that the new CP search method in many cases returns a more precise solution than its previous versions. The new method is able to find and eliminate more field stars in the sample and is not biased towards distant stars. The CP solution for the Hyades open cluster is in excellent agreement with previous determinations.

DEEP VLA IMAGES OF THE HH 124 IRS RADIO CLUSTER AND ITS SURROUNDINGS, AND A NEW DETERMINATION OF THE DISTANCE TO NGC 2264

We present new deep (σ ~ 6 μJy) radio images of the HH 124 IRS radio cluster at 4.8 and 7.5 GHz. We detect a total of 50 radio sources, most of them compact. Variability and spectral indices were analyzed in order to determine the nature of the sources and of their radio emission. A proper motion study was also performed for several of these radio sources using previously reported radio observations. Our analysis shows that 11 radio sources can be associated with Galactic objects, most of them probably young stars. Interestingly, 8 of these sources are in an area less than 1 arcmin2 in size. The importance of such compact clusters resides in that all of its members can be observed in a single pointing with most telescopes and are, therefore, ideal for multi-wavelength studies of variability. Another 4 of the detected sources are clearly extragalactic. Finally, we propose from statistical arguments that out of the remaining sources, about 10 are Galactic, but our study does not allow us to identify which of the sources fall in that specific category. The relatively large proper motions observed for the sources in HH 124 IRS suggest that this region is located at about 400 pc from the Sun. This is significantly smaller than the ~800-900 pc distance usually assigned to the nearby open cluster NGC 2264 with which HH 124 is thought to be associated. However, a reanalysis of the Hipparcos parallaxes for members of NGC 2264, a convergent point approach, and a kinematic analysis all argue in favor of a distance of the order of 400 pc for NGC 2264 as well.

Origin of the wide-orbit circumbinary giant planet HD 106906 - A dynamical scenario and its impact on the disk

A giant planet has been recently resolved at a projected distance of 730 au from the tight pair of young (

VARIABLE RADIO EMISSION FROM THE YOUNG STELLAR HOST OF A HOT JUPITER

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Evolution of the T Tauri star population in the Lupus association

13 Myr) intermediate-mass stars HD 106906AB in the Lower Centaurus Crux (LCC) group. The stars are surrounded by a debris disk which displays a ring-like morphology and strong asymmetries at multiple scales. We aim at studying the likelihood of a scenario where the planet formed closer to the stars in the disk, underwent inward disk-induced migration, and got scattered away by the binary star before being stabilized by a close encounter (fly-by). We performed semi-analytical calculations and numerical simulations (Swift_HJS package) to model the interactions between the planet and the two stars. We accounted for the migration as a simple force. We studied the LCC kinematics to set constraints on the local density of stars, and therefore on the fly-by likelihood. We performed N-body simulations to determine the effects of the planet trajectories (ejection and secular effects) onto the disk morphology. The combination of the migration and mean-motion resonances with the binary star (often 1:6) can eject the planet. Nonetheless, we estimate that the fly-by hypothesis decreases the scenario probability to less than

Proper motion survey and kinematic analysis of the ρ Ophiuchi embedded cluster

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